Drum brakes operate on the principles of converting kinetic energy into heat by creating friction when a set of brake shoes or pads press against an inner surface of a rotating brake drum. However, a common problem with such drum brakes is that uneven mechanical and thermal stresses and uneven cooling tends to cause premature drum cracking (heat cracks) and elevated brake temperatures tend to reduce lining life on brake shoes.
With respect to temperature, it is known that the larger the temperature gradient over a short space, the higher the resulting tension in the material. To combat this, some drums have incorporated narrow cooling fins along the outside of the drum to mitigate this effect, although this has been met with only modest results.
With respect to the mechanical stresses, excess stress is caused when the drum begins to exhibit what is called ‘bell mouthing,’ which occurs when the open end of the drum experiences a greater degree of expansion than does the hub end of the drum. Such uneven drum expansion places a tremendous amount of mechanical stress on the drum, which again tends to cause cracking and a general reduction of useful life.
Therefore, what is needed is a drum design which alleviates the aforementioned mechanical and thermal stresses that are experienced by the drum of a drum brake.